Life Under the Broken Ice

In the balmy Antarctic summer of 2002, a Rhode Island–sized chunk of the Larsen Ice Shelf collapsed, sending thousands of icebergs into the surrounding Weddell Sea. While scanning the ocean bottom for clues to the breakup, geologists made a surprising discovery: A once-hidden community of microbes and clams was thriving in one of the most forbidding places on Earth. "It's an extreme within an extreme community," comments Jim Barry, a benthic ecologist at the Monterey Bay Aquarium Research Institute in Moss Landing, California, who was not involved.

Similar deep-sea ecosystems have been found throughout the world, but this is the first example in Antarctica. Sheltered in a submerged glacial valley 850 meters deep, the ecosystem consists of white, bumpy mats of microbes, as well as clusters of large clams circling small mounds of bubbling mud. The lead scientist on the expedition, glacial geologist Eugene Domack of Hamilton College in Clinton, New York, postulates that, like many deep-sea communities, the microbes derive energy from methane or sulfide in the seawater and sediments, rather than sunlight. They describe the find in this week's Eos, the magazine of the American Geophysical Union.

But the assemblage of species found in the Larsen ecosystem may be unique because Antarctica is isolated by the surrounding circumpolar current, which limits species diversity within the Southern Ocean. In addition, the researchers suggest that the methane fueling the ecosystem derives from nonorganic sources deep inside Earth. That would contrast with most other "cold seep" communities, in which carbon and energy come from microbial recycling of organic remains.

If the Larsen ecosystem utilizes such a source of this "new" energy, it could be a very important discovery, says David Karl, a microbial oceanographer at the University of Hawaii in Honolulu. But, he emphasizes, determining which energy pathway actually drives the Larsen ecosystem will require considerably more evidence. Scientists may need to hurry to acquire that evidence, as sediment once held back by the ice shelf now threatens to bury the ecosystem, Domack says. He hopes to revisit the site in 2007 with a team of experts to study the ecosystem more thoroughly.